Electrophotographic copying, printing or reproducing method

ABSTRACT

The invention relates to an electrostatic copying method by which non-conductive images on an original are reproduced. An image forming member is used of such resistivity and thickness that charge applied to one surface is retained thereon, but can be discharged through the thickness of the material when a discharge path is provided at the opposite surface. When such discharge path is provided and the image forming member is charged, the first surface thereof will be discharged in areas opposite the conductive path, but will retain its charge in other areas.

United States Patent Shreeve 3,770,4 4 Nov. 6, 1973 ELECTROPHOTOGRAPHIC COPYING, PRINTING OR REPRODUCING METHOD Nicholas Gilbert Shreeve, Conkers, Elgin Road, Weybridge, England Filed: June 28, 1971 Appl. No.: 157,544

Inventor:

US. Cl. ll7/37'LE, ll7/17.5 Int. Cl. G03g 13/08, G03g 13/10 Field of Search 117/175, 37 LE;

96/1 R, 1 SD, 1.3; 118/637 References Cited UNITED STATES PATENTS 6/1971 Allinger et al. 117/17.5 8/1964 Hope et al. 117/l7.5

Primary ExaminerWilliam D. Martin Assistant Examiner-M. Sofocleous Attorney-Fleit, Gipple & Jacobson [57] ABSTRACT 9 Claims, 2 Drawing Figures ill ELECTROPHOTOGRAPHIC COPYING, PRINTING OR REPRODUCING METHOD This invention relates to a method of forming electrostatic images, a copying method involving the step of forming electrostatic images, and apparatus for performingthese methods.

In conventional electrostatic copying methods a photoconductive surface or layer is used and an electrostatic charge is produced on or in the said layer, which is then selectively discharged by the illumination of the charged surface or layer by a light-dark pattern to form a latent electrostatic image corresponding to the dark areas which can then be developed so that the developed image can be'utilised to form a copy of the original illuminated pattern. In order for these methods to work, it is necessary to carry out the essential stages in the dark, a necessity which makes the equipment required both expensive and complicated.

According to one aspect of the present invention there is provided a method of forming an electrostatic image including the steps of:

a. uniformly electrostatically charging one surface of an image forming member of a material of such resistivity and thickness that charge applied to said one surface is retained thereon, but can be discharged through the thickness of material by providing a discharge path from the surface opposite to the charged surface,

b. contacting the opposite surface 'of the image form-.

ing member with an original having image areas, the original providing a discharge path from the image forming member except in the image areas, whereby the charged surface of the image forming member is not discharged opposite the image areas of the original and is otherwise discharged opposite the original.

The invention also provides a copying method including the step of forming an electrostatic image by the above method, and developing that image with a toner material. In the copying method, the developed image can be fixed on the image forming'meniber, or transferred to a copy sheet and fixed thereon.

The image areas of the original may be defined by recesses in the surface of the, original which do not touch the image forming member when the image forming member isconta'c'ted with the original.

Alternatively the image areas may be non-conductive areas on the surface of the original.

j Further, the image areas of the original may be defined by areas thereof surrounding embossed or raised representations on the original, which areas do not touch the image forming member when 'the image forming member is contacted with the original.

The present invention has the advantage that it does not rely upon the use of a photoco'nductive layer, and

can be performed in full light or in the dark with equal success. The operation of the present invent-ion makes use of the fact that certain materials of selected resistivity will retain an electrical charge inair unless a discharge path is provided, and similarly will retain an electrical charge in insulating liquids whose resistivity is not less than that of the selectedmaterial. For example, a sheet or layer of a suitable material of selected resistivity will pass a charge from its surface or through itself in a perpendicular direction to the surface to a conductive material with which it is in contact, but not if that contact is interrupted by a non-conductive mate- The material from which the image forming member is made must have a resistivity such that the applied charge will be retained unless a discharge path is provided, and which will discharge where such a path is provided. There are a variety of materials which have the necessary characteristics, of which Cellulose Acetate, Cellulose Tri-Acetate and Ethyl Cellulose are examples. Selected materials should suitably be substantially pure and free from any conductive additions or inclusions which might modify the intrinsic properties of the layer, and the surface of the member should suitably be of a smooth. plane character to ensure that close and intimate contact with the original can be obtained.

In general the member should be thin, preferably between 0.001 and 0.005 inch in thickness. The electrostatic charge may be applied to the surface of said member by any known means, such as'a corona discharge from a wire or array of wires held at high te'n- 'sion, or for the application of a plate, roller, edge or similar device held at high tension. The charge applied may be either positive or negative. A positive charge results in a more even ion discharge from a corona wire, and the production of less ozone, an excess of which is considered to be deleterious to health, while a negative charge enables a slightly lower voltage to be used, since the corona starting voltage for a similar condition is less. Since theipresent invention does not rely upon photosensitivity, the choice of polarity is a matter of convenience, and enables an unrestricted choice of developer material to be made.

More effective discharge of the image forming member occurs if a conductive backing plate is urged against the side of the original remote from the image forming member. This plate can either be earthed or raised to an opposite potential to induce ion flow onto the surface of the image forming member.

.The original from which this copy is to be made may take a variety of different forms. When a sheet of paper or other material is printed or typed, the typeface or printing leaves an impression in the paper; this applies to mostforms or printing other than offset processes,

all formsof typewriting and most forms of handwriting,

more especially when a ball point pen or pencil is used. If another member such as an image forming member, is laid over a conductive original in close contact, small pockets or air are formed which are sufficiently resistant to prevent the discharge of an electrostatic charge. Thus such typewritten paper and handwritten paper can be copied by the inventive method. The neate'r and cleaner the impression, the more effective the insulating gap, and the better and subsequent image; it has been found that the preferred impression has a depth of more than 0.02 mm.

It will also be appreciated that the nature of an ink used on the original, if printed matter, may of itself be non-conductive, and this is particularly the case where raised matter isused, such as thermosetting inks frequently used for commercial letter headings. Thus,

originals having non-conductive images can be copied by the inventive method. Furthermore, embossed characters prevent the continuous contact between an image forming layer and a conductive member, thus forming a linear type of air pocket around the edges of the character embossed. The original is not limited to being in the form of a printed or embossed sheet of paper or similar material, but may consist of any other conductive material, and furthermore may be a template specially formed to give the desired effect, or it may be any manufactured article such as a coin or clock face which provides an embossed or recessed surface in a conductive material. It will be readily apparent that the texture and smoothness of the surface of the original will have an effect upon the degree of contact which can be achieved between the image forming member and the original, and also that the uniformity of the constitution of the original can effect the rate of discharge. It is therefore preferable that the original should have as smooth a surface as possible, and that it should be as uniform as possible.

In order that this invention may be more clearly understood, the following description is given, merely-by way of example, with reference to the accompanying drawings, in which:

FIG. 1 illustrates the operation of the method of this invention; and

FIG. 2 is a schematic illustration of one form of copying apparatus employing this invention.

As shown in FIG. 1, an image forming member 1 in intimate contact with a conductive original 2, which is itself in close contact with a conductive base plate 3. Indentation represents the impress of a character of an image and forms an air pocket between image forming member 1 and original 2. An electrostatic field is created between corona wire 4 which is at high unipolar positive voltage and the conductive base plate 3 which is connected to earth, thereby causing a flow of positive ions from the source 4 to the surface of the image forming member 1. Where there is a direct conductive path through which the ions can flow, as shown at path 6, these electrostatic forces discharge to earth, but where the ions encounter a non-conductive path as typified by the air pocket at 5, the ions are retained on v the surface of the image forming layer; thereby creating a latent electrostatic image 7, corresponding to the character 5. This may be developed subsequently. It will be appreciated that, although in the majority of cases the medium in which this method is performed is air, the principle applies equally in other nonconductive gases and liquids. Thus, if a suitably nonconductiv'e liquid-toner system is interposed between the charge source 4 and the image forming surface 1, then toner is deposited from the liquid carrier onto the latent electrostatic image, and that if, as is normal, the toner is itself non-conductive, the image intensifies itself.

The embodiment of the apparatus illustrated in FIG. 2 comprises a main housing 50 having at its lower left hand edge an opening into which a drawer 22 is slidable. The drawer 22 has a compartment 53 at its outer end, which has a hinged flap 52, and in which is contained a roll 51 of image forming material suitable for performing the invention. The image forming material is, as shown unwound from the roll to extend along a channel in the bottom of the drawer tothe inner edge, then extending backwards over the drawer to cover at 54, in the operational position shown, an original 55 to be copied and which is suitable for copying by the inventive method. The original is itself covering a conductive base plate 57, supported on springs 56 on the upper side of the channel in the bottom of the drawer. Although not in fact so shown for the sake of clarity, the original 55 will of course contact the base plate 57 and image forming member 54.

There is an abutment 23 at the lower edge of the opening in the housing 50. Above this abutment is a cleaning roller 28 which is vertically movable into and out of contact with the image forming member.

The path of travel of the drawer into the housing is substantially horizontal. Above the path of travel is firstly a compression roller 71 spring urged downwardly so that on passing it the image forming member will be urged against the original. Secondly, on the path of travel, is a charging assembly 8 to apply an electrostatic charge to the upper surface of the image forming member. Because the base plate 57 in the drawer will be earthed, on passing beneath the charging assembly 8 the image forming member will, in accordance with the invention, be given a charge pattern in accordance with the image on the original. Adjacent the charging assembly is a developer assembly 9, which as shown comprises an inner tube 10 through which a cloud of toner may removed, blown and an outer suction tube 12. The toner flows from tube 10 to tube 12, so that unwanted powder is remobed, contacting the image forming member and being attracted to the charged areas thereof. Further inward movement of the drawer brings the image forming member into contact with a transfer cylinder 18 which, preferably, has a glass surface and an internally located transfer corona station 14 which assists in transferring the developed image to the transfer cylinder. The cylinder is rotatable, and, at a second transfer position, will re-transfer the image to a copy sheet supplied from a stack 15 by a roller 16. The sheet is urged by transfer roller 17 against the cylinder, and can then be passed to a fixing unit having heaters 19 and to an exit 21.

The drawer can be kept in its most inward position when the machine is not in use. It is supported during inward sliding on a rail 27.

Area 29 may be utilised for housing drive means, controls and an air circulation system which, although not shown in detail, not only operates the developer station 9 but also provides suction at a cleaning station 35 for the transfer cylinder and at the cleaning roller 28. It also provides a constant air flow through heaters 19, to prevent a copy sheet actually touching the heaters, while directing the heat towards the copy sheet. When a copy sheet is not being fixed, air will flow out through louvres in a lid 26 to the fixing station.

The image forming material can be used many times, but the roll facility enables rapid replacement should this be required, or the production of transparancies as will be described below.

The apparatus operates as follows. Normally, the image forming layer is lifted like a lid or flap to enable the conductive original to be positioned on the copper plate. The drawer is then urged forward, either manually or automatically. The surface of the image forming layer passes under compression roller 71, which, together with the compression springs 56, forces the image forming layer 54, the original 55 and the copper base plate 57 into close and intimate contact. This sandwich then passes under the corona charging assembly 8 which applies an electrostatic charge to the surface of the image forming layer, and thereby creates an electrostatic image in accordance with the method of this invention. The layer sandwich then passes under developer unit 9.

If it is desired to produce a transparency, the drawer is returned at this stage, means being provided, as will be seen, to clear roller 71, and a transparency selection switch (not shown) serving also to raise cleaning roller 28. The film bearing the unfixed image can then be cut and removed. By raising the flap 26, to which is attached a fusing plate, the image can be fused or fixed by means of heaters 19.

Normally, however, the drawer will continue forward and the image forming layer together with the developed image will come into contact with glass transfer cylinder 18 which rotates in, as shown, direction A. In-

with a depth control for the sprung copper base plate.

There may also be provided thin foils of copper or aluminum electrically connected woth the copper base plate for insertion between the sheets aboutto be copied, where there are more than one. It will be appreciated that the method described is suitable for copying originals bearing impressions on both sides provided that, as is invariably the case, the originals, are conductive in all directions.

It is, of course, evident that there are many other mechanical arrangements by which the present invention can be made to operate, and the above example is illustrative only and not limiting.

side theglass cylinder 18 there is provided a transfer corona 14, which transfers the developed image from the member 54 to the surface of the glass cylinder. On completion of its in run, after all the imaged area has passed under the cylinder, the drawer 22, which is supported by catches on a slide rail clears the end of the rail 27 so that the inner edge of the drawer drops, thus ensuring that the glass transfer cylinder 13 and the pressure roller 7 are cleared on the return journey. The glass transfer cylinder continues to rotate and a copy sheet (which is here shown as a cut sheet, but which could equally be in roll form) is fed onto the cylinder under transfer roller 17 to coincide with the arrival of the image area. Transfer of the developed image to the copy paper is effected by application of a bias or high voltage potential to roller 17. It should be noted at this stage that the two corona stations 8 and 14 and the transfer roller 17 are all maintained at the same polarity from the same power supply unit. The image bearing copy paper then passes past the heaters 19and out through the copy exit 21. The glass transfer cylinder continues to rotate past cleaning station 15, where any residual traces of toner are removed, although it should be stated that transfer is almost complete.

As the drawer 22 is withdrawn, it clears the pressure roller 7, on which it might otherwise deposit toner which would be inappropriately applied on the next forward passage. Cleaning roller 28 the movement of which depends on the position of the drawer is at this stage pressed down on the image forming member to clean off any residual traces of toner, although here again, transfer is almost complete. At the end of the return journey, after the last of the image area has passed the pressure roller 7 and the cleaning roller 28, the inner edge of the drawer 22 is lifted up by step 23, so that the catches engage once more on the forward slide rails, and roller 28 is simultaneously lifted clear of the surface for the next forward run.

The air flow through the heaters 19 prevents the heat from affecting the image forming layer, for most suitable materials for this purposeare heat sensitive, both with regard to their conductivity and their stability, the hot air passing through the perforations and out through louvres provided in lid 26.

Not described above, but suitable additional features are a guillotine for cutting paper if a roll instead of cut sheets .is chosen for the copy paper, and a facility for copying from thick originals or books with suitable impressions. In this case, a deeper drawer is provided,

The following examples are given in illustration of operation of the method of this invention.

EXAMPLE 1.

A sample typescript was prepared upon a piece of gsm gloss finished paper sold .under the name of Kromekote by theClyde Paper Co. Ltd. by typing without a ribbon to give a-clear impression. This paper is a chrome faced paper of high gloss, of a type which is particularly suitable for performing the invention, because the high gloss allows intimate contact with the image forming member, while the chrome coating is, comparatively, very conductive. This paper represented the conductive original, and it was placed upon a flat polished copper plate which was connected to earth, with the impression facing upwards. This'was then covered by a thin sheet of Ethyl Cellulose, the image forming member, 0.003 inch thick, and the three layers were pressed together in intimate contact. The whole was then subjected to a positive corona discharge from a single strand corona wire positioned about 1.00 inch above the image forming member and maintained at a unipolar voltage of 10 KV. The voltage was then switched off and a clear positive image developed with a positive electrostatic toner, in this case a proprietary toner marketed by Rank-Xerox Limited,

and surplus toner was removed by blowing. The image.

thus obtained was a clear reproduction of the original typescript, which was then fused on to the cellulose sheet by heat, thus forming a transparent copy suitable for projection or reproduction by conventional means.

EXAMPLE 2 An image was prepared as in Example 1, and a piece of ordinary paper placed upon the developed image. The voltage was then switched to the corona wire, and the image electrostatically transferred to the paper, to which it was then fused. In this case the image was reversed, and it will be appreciated that the technique could be readily utilised for the production of masters for offset printing.

EXAMPLE 3 An image was prepared as described in Example 1,

and then transferred to a sheet of glass by the application of an electrostatic field as described in Example 2, and the transferred image was then re-transferred in a similar way to a piece of copy paper thus producing a right reading print similar to the original typescript on the copy paper.

In the above examples it will be appreciated that a variety of toners could be used, as well as a variation in the polarity of charging. Also, there are many materials which can be used for the transfer process but it has been found that glass works particularly well.

EXAMPLE 4 An arrangement of layers similar to that described in Example 1 was prepared and placed in a shallow glass dish, and covered with a dispersion of a proprietary liquid toner concentrate, in this case as marketed by Smith-Corona-Merchant Ltd., in Freon. On exposure to a negative corona discharge, toner concentrate was precipitated onto the surface of the image forming member corresponding to the characters impressed in the conductive member. The seal between the layers was sufficient to prevent the original from being wetted.

I claim:

1. An electrostatic copying method including the steps of taking an image forming member of such resistivity and thickness that electrostatic charge applied to one surface thereof is normally retained thereon, but is locally dischargeable through the thickness of the material upon provision of a discharge path from the surface of the image forming member opposite to the charged surface, the discharge being only from a region of the charged surface opposite the locality of the discharge path; taking an original having an image area and a non-image area capable of providing a discharge path from said image forming member when contacted therewith; contacting said image forming member with said original; applying a charge uniformly to said one surface of the image forming member while its opposite surface is contacted by said original, said original providing at its non-image area only a discharge path from said opposite surface of said image forming member whereby the image forming member retains a charge only opposite the image areas of the original, and thereafter developing the electrostatic image on the image forming member with a toner material.

2. A method as claimed in claim 1 wherein said one surface of said image forming member is charged by corona discharge.

3. A method as claimed in claim 1 wherein a conductive backing plate is urged a'gainst the side of the original remote from the image forming member.

4. A method as claimed in claim 1 wherein the image forming member is made of one of the group comprising cellulose acetate, cellulose tri-acetate and ethyl cellulose, and is between 0.001 and 0.005 inch thick.

5. A method as claimed in claim 1 wherein the image areas of the original are defined by recesses in the surface of the original which do not touch the image forming member when the image forming member is contacted with the original.

6. A method as claimed in claim 5 wherein the original is paper, and the recesses are impressions made with a typewriter, and are more than 0.002 mm deep.

7. A method as claimed in claim 1 wherein the image areas of the original are non-conductive areas of the surface of the original.

8. A method as claimed in claim 1 wherein the image areas of the original are defined by areas thereof surrounding raised representations on the original, which areas do not touch the image forming member when the image forming member is contacted with the original.

9. A method as claimed in claim 1 including the further step of locating a non-conductive liquid toner system at the side of the image forming member which is charged. 

2. A method as claimed in claim 1 wherein said one surface of said image forming member is charged by corona discharge.
 3. A method as claimed in claim 1 wherein a conductive backing plate is urged against the side of the original remote from the image forming member.
 4. A method as claimed in claim 1 wherein the image forming member is made of one of the group comprising cellulose acetate, cellulose tri-acEtate and ethyl cellulose, and is between 0.001 and 0.005 inch thick.
 5. A method as claimed in claim 1 wherein the image areas of the original are defined by recesses in the surface of the original which do not touch the image forming member when the image forming member is contacted with the original.
 6. A method as claimed in claim 5 wherein the original is paper, and the recesses are impressions made with a typewriter, and are more than 0.002 mm deep.
 7. A method as claimed in claim 1 wherein the image areas of the original are non-conductive areas of the surface of the original.
 8. A method as claimed in claim 1 wherein the image areas of the original are defined by areas thereof surrounding raised representations on the original, which areas do not touch the image forming member when the image forming member is contacted with the original.
 9. A method as claimed in claim 1 including the further step of locating a non-conductive liquid toner system at the side of the image forming member which is charged. 